I haven't done it yet, so I probably shouldn't give advice! I am planning a Carpenter's star that will be a "controlled scrappy" with my fabrics all from the same color famikly, but varying in value. I figure if I keep the background unified, and alternate dark/medium-dark with light/ medium-light I'll get the 3-D effect.
So I say separate your layer cake fabrics into value groups, and go from there!
Alison